The immune system becomes deranged during aging. Autoimmune and neoplastic disease, occurring frequently in old experimental animals and man, may result from immune dysfunction. The proposed program is designed to continue a multidisciplinary study of the immunobiology of aging. The program is a collaborative effort of the Sloan-Kettering Institute and Cornell University Medical College. Definitive studies of the structure, function and pathology of the immune system during aging, nutritional influences on lifespan and on the diseases of aging and the immunobiology of trisomy 21 (Down's syndrome) will be carried out in studies involving 17 professional investigators in the two institutions.